fix(agent): keep explicit skills out of system prompt

nanobot/agent/context.py

@@ -94,7 +94,6 @@ class ContextBuilder:
     def build_system_prompt(
         self,
         *,
-        active_skill_names: Sequence[str] | None = None,
         channel: str | None = None,
         session_summary: SessionSummary | None = None,
         workspace: Path | None = None,
@@ -119,11 +118,6 @@ class ContextBuilder:
                 parts.append(f"# Memory\n\n## Long-term Memory\n{memory}")
 
         active_skills = self.skills.get_always_skills()
-        active_skills.extend(
-            name
-            for name in (active_skill_names or ())
-            if name not in active_skills
-        )
         if active_skills:
             active_content = self.skills.load_skills_for_context(active_skills)
             if active_content:
@@ -165,6 +159,33 @@ class ContextBuilder:
 
         return "\n\n---\n\n".join(parts)
 
+    def build_runtime_context_blocks(
+        self,
+        current_message: str,
+        blocks: Sequence[RuntimeContextBlock] | None = None,
+    ) -> list[RuntimeContextBlock]:
+        """Add explicitly invoked skill instructions to this turn's runtime context."""
+        merged = list(blocks or ())
+        invoked = self.skills.get_explicitly_invoked_skills(current_message)
+        if not invoked:
+            return merged
+        always_active = set(self.skills.get_always_skills())
+        skill_names = [name for name in invoked if name not in always_active]
+        skill_content = self.skills.load_skills_for_context(skill_names)
+        if not skill_content:
+            return merged
+        skill_block = RuntimeContextBlock(
+            source="explicit_skills",
+            content=(
+                "[Active Skills — instructions for this user turn]\n"
+                f"{skill_content}\n"
+                "[/Active Skills]"
+            ),
+        )
+        if skill_block not in merged:
+            merged.append(skill_block)
+        return merged
+
     @staticmethod
     def _without_duplicate_session_summary(
         entries: list[dict[str, Any]],
@@ -279,16 +300,10 @@ class ContextBuilder:
     ) -> list[dict[str, Any]]:
         """Build the complete message list for an LLM call."""
         root = workspace or self.workspace
-        active_skill_names = (
-            self.skills.get_explicitly_invoked_skills(current_message)
-            if current_role == "user"
-            else []
-        )
         messages: list[dict[str, Any]] = [
             {
                 "role": "system",
                 "content": self.build_system_prompt(
-                    active_skill_names=active_skill_names,
                     channel=channel,
                     session_summary=session_summary,
                     workspace=root,
@@ -332,7 +347,11 @@ class ContextBuilder:
     ) -> dict[str, Any]:
         """Build only the fresh turn message without merging it into history."""
         content = self.build_user_content(current_message, image_paths=media)
-        blocks = list(runtime_context_blocks or ()) if current_role == "user" else []
+        blocks = (
+            self.build_runtime_context_blocks(current_message, runtime_context_blocks)
+            if current_role == "user"
+            else []
+        )
         merged, runtime_context_meta = append_runtime_context(content, blocks)
         current: dict[str, Any] = {"role": current_role, "content": merged}
         if current_role == "user" and runtime_context_meta is not None:

nanobot/agent/loop.py

@@ -797,7 +797,10 @@ class AgentLoop:
         ]
         blocks = runtime_context_blocks_from_metadata(request.metadata)
         blocks.extend(await resolve_runtime_context(providers, request))
-        return blocks
+        return self.context.build_runtime_context_blocks(
+            request.original_user_text or "",
+            blocks,
+        )
 
     async def _dispatch_command_inline(
         self,

tests/agent/test_context_builder.py

@@ -407,15 +407,20 @@ class TestBuildMessages:
         builder = _builder(tmp_path)
 
         messages = builder.build_messages([], "Please $review this patch and use $review carefully.")
+        plain_messages = builder.build_messages([], "Please review this patch carefully.")
 
         system_prompt = messages[0]["content"]
-        assert "# Active Skills" in system_prompt
+        user_prompt = messages[-1]["content"]
-        assert "### Skill: review" in system_prompt
+        assert system_prompt == plain_messages[0]["content"]
-        assert "Follow the unique review checklist." in system_prompt
+        assert "Follow the unique review checklist." not in system_prompt
-        assert system_prompt.count("### Skill: review") == 1
+        assert "Please $review this patch" in user_prompt
-        assert messages[-1]["content"] == (
+        assert "[Active Skills — instructions for this user turn]" in user_prompt
-            "Please $review this patch and use $review carefully."
+        assert "### Skill: review" in user_prompt
-        )
+        assert "Follow the unique review checklist." in user_prompt
+        assert user_prompt.count("### Skill: review") == 1
+        assert messages[-1]["_meta"]["runtime_context"]["sources"] == [
+            "explicit_skills"
+        ]
 
     def test_unknown_skill_reference_does_not_change_active_skills(self, tmp_path):
         messages = _builder(tmp_path).build_messages([], "Keep the shell literal $HOME.")

tests/agent/test_loop_runner_integration.py

@@ -146,6 +146,16 @@ async def test_runtime_context_is_persisted_as_next_turn_prompt_prefix(tmp_path)
     from nanobot.bus.events import InboundMessage
     from nanobot.bus.queue import MessageBus
 
+    skill_dir = tmp_path / "skills" / "review"
+    skill_dir.mkdir(parents=True)
+    (skill_dir / "SKILL.md").write_text(
+        "---\n"
+        "name: review\n"
+        "description: Review changes.\n"
+        "---\n\n"
+        "Follow the unique review checklist.",
+        encoding="utf-8",
+    )
     provider = MagicMock()
     provider.get_default_model.return_value = "test-model"
     provider.generation = GenerationSettings()
@@ -169,7 +179,7 @@ async def test_runtime_context_is_persisted_as_next_turn_prompt_prefix(tmp_path)
         channel="cli",
         sender_id="user",
         chat_id="direct",
-        content="first turn",
+        content="first turn $review",
     ))
     await loop._process_message(InboundMessage(
         channel="cli",
@@ -184,6 +194,9 @@ async def test_runtime_context_is_persisted_as_next_turn_prompt_prefix(tmp_path)
     second_wire = LLMProvider._sanitize_empty_content(second_request)
     assert second_wire[: len(first_wire)] == first_wire
     assert first_wire[1] == second_wire[1]
+    assert first_wire[0] == second_wire[0]
+    assert "Follow the unique review checklist." not in first_wire[0]["content"]
+    assert "Follow the unique review checklist." in first_wire[1]["content"]
     assert second_wire[2]["role"] == "assistant"
     assert second_wire[2]["content"] == "first answer"
     assert second_wire[3]["content"].startswith("second turn")
@@ -191,7 +204,7 @@ async def test_runtime_context_is_persisted_as_next_turn_prompt_prefix(tmp_path)
 
     persisted_first_user = session.messages[0]
     assert persisted_first_user["content"] == first_wire[1]["content"]
-    assert public_history_message(persisted_first_user)["content"] == "first turn"
+    assert public_history_message(persisted_first_user)["content"] == "first turn $review"
 
 
 @pytest.mark.asyncio